The present invention relates to internal combustion engines and in particular to oil rings used on the pistons of such engines.
On a conventional internal combustion engine, the pistons are mounted for reciprocating motion in cylinder bores and are sealed with respect thereto by one or more piston rings located within circumferential grooves adjacent the head of the piston. Lubrication of the cylinder walls is conventionally achieved by means of the oil mist which is produced within the crankcase. An oil ring is normally located in a circumferential groove below the piston rings and on the downstroke of the piston will control the film of oil on the cylinder wall, so that there is sufficient oil to minimise wear while excess oil will not pass the piston rings to be burnt in the cylinder. Such oil rings are formed from resilient metal and are split so that they engage the wall of the cylinder under compression. The outer face of the oil ring which engages the cylinder wall has upper and lower lip formations with a recess therebetween, apertures being provided in the recess and through the piston wall for return of excess oil. In a typical engine of this form, the oil ring may contribute up to 30% of the total engine frictional forces.
The present invention provides means for reducing the frictional forces produced by the oil ring.